But I don't know if CC developpers already know the problem and intend to correct it.It is unlikely that it will be solved any time soon, if ever.
However, you can avoid the hairlines using one of two workarounds:
1) Make sure there's a 1 pixel transparent border on all 4 sides of the images. (This is an option for TiledBackground4 only in your example)
2) Change sampling in the runtime properties from "linear" to "point". (This is an option for all the TBs, but will have influence on the visual presentation of stretched graphics)
EDIT: Technically, what you see by those hairlines are fragments of the other side of the images, and you see them because of the linear sampling (which works sub-pixel) and because the images wrap around (that's the purpose of a TB)